1. Field of the Invention
The present invention relates to a dental diamond bur to be mounted in a dental handpiece, which is suitable for cutting safely and precisely a hard tissue of tooth, from which a tectorium portion thereof has been removed for the purposes of exposure and opening of an occlusal surface side of a pulp chamber filled with a dental pulp, within a short period of time, prior to a root canal treatment such as treatment of pulp removal, enlargement of a root canal, and filling medicine, in the dental remedy.
2. Description of the Conventional Art
In the dental root canal treatment, it is the most important to treat surely a root canal. In this root canal treatment, a dental cutting tool that is mounted in a dental handpiece to use, is used for not only cutting out of a tectorium portion of tooth and a horn of pulp chamber but also opening of a pulp chamber and spreading of a root canal, and is applied for a pretreatment of the enlargement of a root canal by a reamer or a file for the purposes of treatment of pulp removal by means of a cleanser, filling medicine, etc. to be carried out later. However, the shape of the pulp chamber or root canal is different between anterior teeth and molars. Further, it is also different among individuals. In addition, the pulp chamber or the interior of root canal becomes narrow by increased impaction of a secondary dentin by an increase in age. For these reasons, the shape of the pulp chamber or root canal is not in a definite form. Moreover, since the pulp chamber or root canal is positioned within a tooth, it is difficult to carry out the opening or enlargement under observation by naked eyes, and it is not easy to carry out the root canal treatment precisely within a short period of time.
Hitherto, as the dental cutting tool for root canal treatment, which is mounted in a dental handpiece and used for cutting out a tooth, have been employed burs having various forms such as a dental diamond bur in which diamond grains are electro-deposited on a stainless steel bar by plating, and a dental carbide bur in which a spiral blade or furrow is formed with tungsten carbide. However, in recent years, the dental diamond bur having good cutting properties, in which cut pieces are hardly scattered, has been widely used. With respect to the shape of the dental diamond bur for root canal treatment, are widely used a round-end bur having a spherical end and a hemispherical cone bur having a hemispherical cone-shaped end.
The root canal treatment using such dental diamond bur is carried out in the following procedures. That is, first of all, a dental caries portion and a tectorium portion are cut out and removed; the tectorium portion is completely removed from a lingual side in the case of anterior teeth and from an occlusal surface side in the case of molars, respectively, using a round-end bur or a hemispherical cone bur; and a horn of pulp chamber is subsequently removed, thereby making it easy to perform extirpation of pulp by a cleanser and enlargement of a root canal by a reamer or a file.
In this case, when the round-end bur having a spherical end is used, after perforating into the pulp chamber, the horn of pulp chamber is removed by scratching up by a shoulder of the round-end bur, thereby opening the pulp chamber. However, the aperture surface of tooth cut out by the round-end bur is liable to become in a rounded uneveness shape. As a result, when a filler is packed within the spread root canal later, the adhesion in a pulp cavity is possibly deteriorated. On the other hand, when the hemispherical cone bur is used, a transitional portion from the pulp chamber to the root canal does not become in a continuous flare shape, causing to form a difference in level. As a result, the operation by a reamer or a file to be effected later is liable to be adversely affected. Further, in the case of opening of pulp chamber, such as maxillary first molars, maxillary premolars, and mandibular anterior teeth, the teeth are often strongly flattened under pressure in a near centrifugal manner from the neighborhood of a cervix toward a root apex. As a result, in the vicinity of a root canal orifice, there is a danger that perforation occurs from a pulp chamber wall or a pulp chamber floor.
In recent years, for the purpose of preventing the perforation from occurrence, has been developed a dental diamond bur in a hemispherical cone shape, provided with a bare head portion where a ground surface ground of a stainless steel is exposed, without diamond grains being attached in a portion of about 1 to 3 mm from a tip thereof. In this dental diamond bur, since diamond grains are not attached to the tip thereof, the teeth are not cut out by the tip portion, and the perforation less possibly occurs even in the operation by an operator on a basis of the touch of fingers. However, since the currently commercially available dental diamond bur in a hemispherical cone shape having a bare head portion is in a tapered form in which the shape of the diamond grains-attached portion as a working portion becomes narrow at a constant rate toward the tip, a tooth surface cut out becomes also in a linear shape. In addition, in the case where the tectorium portion of tooth is cut out by a central portion or tip side of the dental diamond bur, a rear end portion of the dental diamond bur contacts with a tooth aperture portion and cuts it. As a result, the cutting-out amount of the tooth aperture portion becomes high more than necessary. Accordingly, with respect to the currently commercially available dental diamond bur, one that can be suitably used for the treatment including from the opening of a pulp chamber to the spreading of a root canal orifice is not present.
The present invention is aimed to provide a dental diamond bur, which is applicable for operations including from opening of a pulp chamber to spreading of a root canal orifice to any teeth of anterior teeth and molars; does not cut out a tooth aperture portion more than needed; cuts out a tooth aperture surface into a smooth curve surface form, thereby improving the adhesion between a filler and a tooth in that cut-out site; and is free from occurrence of perforation, in the root canal treatment.
In order to achieve the above-described aim, we, the present inventors made extensive and intensive investigations. As a result, it has been found that when a tip portion of the dental diamond bur is shaped in a body of revolution with a prescribed dimension, not having diamond grains attached thereto and having a convergent smooth curve form, not only perforation is prevented from occurrence, but also it is possible to carry out elimination of a tectorium portion and treatments including from opening of a pulp chamber to spreading of a root canal orifice, while bringing the tip portion into contact with a root canal orifice; and that when a diamond grains-attached portion of the dental diamond bur in a smooth curved continuous form, in which diamond grains are slightly protruded in a tip side thereof, is a body of revolution with an externally convex curve, and a maximum diameter portion thereof is arranged in a prescribed position apart from the tip portion, it is possible to prevent a tooth aperture portion from being cut out more than needed, and a cut-out surface of the tooth orifice portion can be made in a smooth curve surface form, leading to accomplishment of the present invention.
Specifically, the present invention is concerned with a dental diamond bur comprising a tip portion that is a body of revolution with a convergent smooth curve, having a diameter in a shank portion side thereof of 0.5 to 0.8 mm and a height of 0.5 to 0.85 mm; and a diamond grains-attached portion that is a body of revolution with an externally convex curve from a rear end of the tip portion toward a shank portion, a maximum diameter portion of the diamond grains-attached portion being positioned in a range of 5.0 to 10.0 mm from the front end of the tip portion, and the tip portion side of the diamond grains-attached portion constituting a smooth surface in which diamond grains are slightly protruded from the shank portion side of the tip portion. Further, it is preferred that the diamond grains-attached portion is a body of revolution with an externally convex curve having a length of 6 to 11.0 mm and a diameter in the shank portion side of 1.45 to 1.75 mm.